The present invention relates to a float for a towed line, whose field of application is generally seismic measurements at sea, in which a battery of lines carrying acoustic sensors is towed at the stern of a ship. Each of the lines comprises a deflector in front of the sensors, which is a submerged and vertical wing which incurs a transversal lift and maintains the line alongside the wake of the ship, and a float from which the deflector is suspended and whose aim is to prevent the line from sinking under the weight of the deflector.
The floats must be almost insensitive to the disturbances to which they may be submitted, in particular by the sea swell. Unfortunately, as far as this is concerned, the known floats oscillate too easily in the vertical direction following the movements of the swell. The suspension line of the float deflector is submitted to periodic surges which can end by fatigue rupture or can create damage to the connections, and the quality of measurement can also be disturbed. The float to be described below overcomes this disadvantage while still retaining good directional stability, above all in its most advantageous embodiment.
The known floats have a fuselage shape, expanded in the centre and progressively tapered towards the ends. The float according to the invention comprises a horizontal portion of the floating body whose shape is also substantially fuselage shaped, but also an upper part of the floating body, extending from the horizontal portion upwards and with horizontal cross-sections which are closely uniform; in addition, the horizontal portion is completely submerged and the upper portion is partially emerged when the float holds the line, or a heavy element of the latter.
The vertical movement of the sea swell is therefore represented above all by a variation of the immersion of the upper portion without any special force on the float because of the uniformity of its cross-section and the small variation of the submerged volume: the vertical oscillating movement of the float and its load therefore does not have a great amplitude.
The stability is still better if the upper portion is erected at the rear of the horizontal portion, and particularly if the suspension element of the deflector is located in front of the upper portion.
If this suspension element comprises a single articulation around a transversal axis, the float is restrained from rolling movements and comes back into place more easily.
The directional stability of the float is improved if its horizontal portion is wider than its height, which makes it possible to reduce its lateral surface, and thus the lateral disturbing forces.